They’re both six-footers, Wimbledon champs, and powerful, erratic ball-strikers, so it made sense that the semifinal between Petra Kvitova and Venus Williams wasn't decided until the last possible moment. The American started fast, the Czech adjusted in the second set, and the two of them fought tooth and nail, serve and return, forehand and backhand, through an excellent third. Finally, in the tiebreaker that closed it, Venus’s famous weakness, her forehand, let her down and Kvitova survived 3-6, 6-3, 7-6 (2) in 2 hours and 24 minutes.

The knock on Kvitova has always been her radical, whiplash-inducing inconsistency; a blazingly good set will often be followed by an utter fizzle in the next one. But the upside for Petra is that even when she’s playing horribly, she knows she might just be a few moments, a few winners, from playing brilliantly again. It’s not surprising that she plays a lot of three-setters, or that she has a knack for coming back and winning matches after losing the first set.

That’s what happened today, but it wasn’t just that Kvitova suddenly went from missing everything to missing nothing. She made adjustments: She mixed her serve up and went to Venus’s forehand side effectively; she used her backhand slice to make her bend; she hit deep and down the middle rather than going for the lines; and she wrong-footed Venus with her backhand down the line on a number of big points. To close it out, though, Kvitova stuck with the basics. When she saw Venus’s forehand breaking down in the tiebreaker, she was happy to keep feeding it.

Williams also adjusted, and that’s what made the third set a compelling struggle. She began to read Kvitova’s serves to her forehand, and she used her own serve, both flat and slice, to get out of trouble. Venus had her chances: She created 13 break point opportunities, but cashed in on just two of them. The biggest of those 11 misses came with Kvitova serving at 2-3 in the third set, 30-40. Venus had a very makeable mid-court forehand that she didn’t quite get all the way up to, and put into the net.

It might have been fatigue; the 33-year-old was coming off a couple of long three-setters, and she wasn’t moving forward quite as quickly as she usually does. But this was still a stellar week for Venus. And the signs are good for Kvitova, who has dropped out of the Top 10, as well. She played within herself today, and she’ll need to do the same in the final, against the German wallboard Angelique Kerber.